Using biomarkers to determine dispersion and cycling of organic matter from the Sepik River, Papua New Guinea

In January 2000, two sediment trap arrays consisting of five stainless steel cylinders (1 m long and 10 cm diameter) fitted into a weighted aluminium frame were deployed for 48 hours on a free drifting mooring in the Sepik Canyon (SC) at depths of 100 and 260 m. During deployment, the mooring drifted 19.5 km north west from the Canyon axis, but remained within the area of the river plume. The mooring was retrieved in approximately 380 m of water and the contents of the sediment traps were drained into 4 L glass bottles. The bottles were shaken and sub-sampled for particulate carbon and the remaining samples were then filtered through pre-weighed 0.45 µm GFF filters, rinsed with MilliQ water to remove salt, and were wrapped in pre-combusted foil, then stored at -20°C. Water samples for lipid analysis were collected with Infiltrex II (TM) high volume samplers. Samplers were attached to the sediment trap mooring at depths of 55, 180, 200 and 220 m. Depths were chosen to target layers of turbidity as detected with the CTD instruments. Each sampler pumped 388- 432 L of seawater before the filters clogged and the pumps shut down. At other offshore stations an Infiltrix sampler was attached to the hydrowire and lowered to sample at 220 m within the undercurrent while the ship drifted. These deployments were short in duration and only sampled about 90 L each time. Samples were collected at Vitiaz Strait (Vitiaz), a region not influenced by the river, and another station (S+2) to the northwest of the river, which may be influenced by it, to determine dispersion and potential entrainment in the 200 m undercurrents. Samples were also collected upstream of the small village of Kopar (SR), at a depth of 1 m below the river surface, in 4 L glass bottles and pumped through an Infiltrex II (TM) sampler on the deck of the vessel. Upon retrieval of the samplers, the GFF filters were removed and packed in glass jars with foil lined lids and stored at -20°C. The XAD2 columns were removed, resealed and stored at 4°C. Samples for marine dissolved lignin analysis were collected using 10 L Niskin bottles attached to a CTD system. Specific depths were targeted, which offshore included the chlorophyll maximum and the depth of the New Guinea Coastal Undercurrent (NGCUC1, NGCUC2) or the Equatorial Undercurrent (EUC1, EUC2) at 220 m. Upon retrieval the Niskin bottles were clamped shut, pressurised with N2 gas and the water was filtered through GFF filters into 4 L glass bottles. The filtered seawater was acidified to pH 2 with concentrated HCl and poured back into the 10 L Niskins. The bottles were again clamped and pressurized and the water forced through prepared cartridges of C18 silica for solid phase extraction of lignin. After sampling, the cartridges were re-wrapped in cleaned foil and stored at 4°C. Riverine dissolved lignin samples were collected using GFF filtration into 1 L glass bottles and frozen at dry ice temperature. In the laboratory, the water was removed using rotary evaporation, leaving a powder for lignin analysis. Surface sediment samples for lignin analysis were collected from 19 sites on the coastal margin (around SC) by gravity and Kasten corers.Additional water samples were collected using Niskin bottles for dissolved and particulate carbon (DOC, POC), nutrient and stable isotope analyses. Riverine samples, collected for lignin analysis, were also analysed to determine organic carbon, total nitrogen, stable carbon isotope ratios and stable nitrogen isotope ratios. Samples collected for lipid analysis were extracted and a subsample taken for determination of total extractable organic matter (EOM). The remaining extracts were reduced and saponified and the neutral lipids extracted and then separated into hydrocarbon and esters plus alcohol/sterol fractions on silica gel. The remaining extract was acidified and the fatty acids were extracted.Alkanes in the hydrocarbon fractions were determined using a gas chromatograph fitted with a flame ionization detector (GC-FID). Polynuclear aromatic hydrocarbon (PAH) analysis was carried out using selected ion monitoring gas chromatography-mass spectroscopy (SIM GC-MS). Sterols and n-alcohols were converted to TMS esters and analysed using full scan gas chromatography/mass spectroscopy (GC-MS). The fatty acid fraction was converted to methyl esters and analysed using GC-FID.Dried riverine and surface sediment samples for lignin analysis were converted to phenols and the lignin-derived phenols separated using GC-MS. Quantification was achieved using SIM GC-MS, This research was undertaken to describe the fate and cycling of organic matter input from the Sepik River into the near coastal waters using molecular markers and to investigate stable biomarkers that might be useful for tracing long range transport. This work is part of Project TROPICS (Tropical River Ocean Processes in Coastal Settings), a joint coastal oceanographic study by Australia, Indonesia, Papua New Guinea, and the USA.2000年1月，两套由5根长1m、直径10cm的不锈钢圆柱（stainless steel cylinders）组成的沉积物捕获器阵列（sediment trap arrays）被安装于配重铝架（weighted aluminium frame）上，于塞皮克海沟（Sepik Canyon, SC）水深100m和260m处的自由漂浮锚系（free drifting mooring）上部署了48小时。部署期间，锚系向西北方向漂移了19.5km，偏离海沟轴线，但仍处于河流羽流（river plume）影响区域内。锚系最终在约380m水深处被回收，沉积物捕获器内的样品被转移至4L玻璃瓶中。将玻璃瓶摇匀后，分取子样用于颗粒碳分析；剩余样品经预称重的0.45μm GFF滤膜（Glass Fiber Filter）过滤，用密理博超纯水（MilliQ water）冲洗以去除盐分，随后用预灼烧过的铝箔包裹，于-20℃下保存。用于脂类分析（lipid analysis）的水样采用Infiltrex II（TM）高体积采样器采集。采样器被安装在沉积物捕获器锚系上，布放水深分别为55m、180m、200m和220m，这些水深均针对温盐深仪（conductivity-temperature-depth, CTD）探测到的浊度层设置。每个采样器在滤膜堵塞、泵体停机前可抽取388~432L海水。在其他离岸站位，Infiltrix采样器被安装在水文缆线上，随船漂移期间被下放至220m水深的潜流层中采样。此类部署持续时间较短，每次仅采集约90L水样。采样站位包括不受河流影响的维提亚兹海峡（Vitiaz Strait, Vitiaz），以及位于该河流西北方向、可能受其影响的S+2站位，用于探究200m潜流中的有机质扩散与潜在夹带过程。此外，在科帕尔村（Kopar）上游的河口区域，于河水面下1m处采集了水样：样品用4L玻璃瓶装载，并通过甲板上的Infiltrex II（TM）采样器进行泵送过滤。回收采样器后，GFF滤膜被取出，装入带有铝箔衬垫盖子的玻璃罐中，于-20℃下保存；XAD-2树脂柱（XAD2 columns）被取下并重新密封，于4℃下保存。用于海洋溶解木质素分析（dissolved lignin analysis）的水样采用安装于CTD系统上的10L尼斯金采水瓶（Niskin bottles）采集。针对特定水深进行采样，离岸站位的采样水深包括叶绿素最大值层、新几内亚沿岸潜流（New Guinea Coastal Undercurrent, NGCUC1、NGCUC2）所在深度，以及220m处的赤道潜流（Equatorial Undercurrent, EUC1、EUC2）。回收采水瓶后，将瓶口夹紧，用氮气加压，将水样经GFF滤膜过滤至4L玻璃瓶中。将过滤后的海水用浓盐酸酸化至pH=2，再倒回10L尼斯金采水瓶中，再次夹紧瓶口并加压，使水样流经制备好的C18硅胶（C18 silica）固相萃取柱（solid phase extraction），以萃取木质素。采样完成后，萃取柱用洁净铝箔重新包裹，于4℃下保存。河流溶解木质素样品经GFF滤膜过滤后收集至1L玻璃瓶中，置于干冰温度下冷冻。在实验室中，通过旋转蒸发（rotary evaporation）去除水分，得到用于木质素分析的粉末样品。用于木质素分析的表层沉积物样品通过重力取样器（gravity corers）和凯斯顿采泥器（Kasten corers）在塞皮克海沟周边的海岸带19个站位采集。额外采集的水样采用尼斯金采水瓶收集，用于溶解有机碳（dissolved organic carbon, DOC）、颗粒有机碳（particulate organic carbon, POC）、营养盐及稳定同位素分析。用于木质素分析的河流样品还被用于测定有机碳、总氮、稳定碳同位素比值及稳定氮同位素比值。用于脂类分析的样品经萃取后，分取子样用于测定总可提取有机质（total extractable organic matter, EOM）。剩余萃取液经浓缩后进行皂化反应，提取中性脂类，随后通过硅胶柱（silica gel）将其分为烃类组分（hydrocarbon fractions）、酯类以及醇/甾醇组分。剩余萃取液经酸化后，提取脂肪酸。烃类组分中的烷烃采用带火焰离子化检测器的气相色谱仪（gas chromatograph fitted with a flame ionization detector, GC-FID）进行测定；多环芳烃（polynuclear aromatic hydrocarbon, PAH）分析采用选择离子监测气相色谱-质谱联用仪（selected ion monitoring gas chromatography-mass spectroscopy, SIM GC-MS）完成；甾醇与正构醇经衍生为三甲基硅酯（trimethylsilyl esters, TMS esters）后，采用全扫描气相色谱-质谱联用仪（full scan gas chromatography/mass spectroscopy, GC-MS）分析；脂肪酸组分经衍生为甲酯（methyl esters）后，采用GC-FID进行分析。用于木质素分析的干燥河流沉积物与表层沉积物样品被转化为酚类物质，采用气相色谱-质谱联用仪分离木质素源酚类（lignin-derived phenols），通过SIM GC-MS实现定量。本研究旨在利用分子标记物描述塞皮克河输入近岸水域的有机质归宿与循环过程，并探究可用于示踪长距离输运的稳定生物标志物。本工作属于TROPICS项目（Tropical River Ocean Processes in Coastal Settings），是澳大利亚、印度尼西亚、巴布亚新几内亚与美国联合开展的海岸海洋学研究的一部分。